Two-stroke internal-combustion motor



May 25 1926.

A. H. 'ROSBORG TWO-STROKE INTERNAL COMBUSTION MOTOR Filed August 30, 1923 Mud/96mm M 2/ Patented May 25, I926;

EJETEE;

TENT GF-FICE.

ANIDIEES HARALI) BOSIBORG, OF STOCKI-IOLM, SWEDEN.

TWO-STROKE INTERNAL-COMBUSTION MOTOR,

Application filed. August 30, 1923. Serial No. 660,067.

It is generally known that in internal combustion motors working on the twostroke principle and the piston of which serves as an a1r pump, compressing air 1n the closed crank case, the effective average pressure in the working cylinder is particularly low, frequently not even half the corresponding average pressure in four-stroke motors. It is clear that this entails large cylinder dimensions which are unsuitably large for a certain effect, which makes the motor heavy and expensive. The cause of the low average pressure is also generally known, viz. the small amount of effective air with which the cylinder is charged. The greatest amount of air available for each piston stroke, the volume of which is equal to the volume traversed by the piston, is reduced partly in consequence of the low volumetric efiiciency of the air pump, partly through the scavenging air which is lost with with the exhaust gases, whereby a quantity of air, which probably is no greater than or of the cylinder volume traversed, remains as charging air, with correspondingly reduced effect for each stroke as compared with the case that the volume of the charging air were equal to the whole of the cylinder volume traversed, as is the case with four-stroke motors. In order to ob tain the increased effect an increased amount of scavenging and charging air is thus required, and therefore the volume of the air pump must be increased eitherby the ex1stiug pump being combinedw th a special auxiliary pump, orby abolishing the pump elfect of every working pistonarranging one or more special air pumps which will supply all the requisite air. In both cases a special receiver for compressed a1r 1s required. The separate a1r pump (or a1r pumps, as the case may be) wlth a comparatively hlgh degree of volumetric eflici-ency may, of course, be dimensioned according to the desired increased a1r quantity.

According to the present invention the vessel receiving compressed air from the said air pump or pumps is the closed crank case of the motor, which crank case is com 111011 to all cylinders of the motor and from which the respective scavenging air channels pass to the cylinders. This offers the following advantages over the customary arrangement of a separate crank case for each cylinder: The common crank case may be made cheaper and plainer, the separate air valves as well as the separate tightening devices round the shaft at every crank case are eliminated, no extra, bulky receiver for compress-ed air is required, and the crank case as a compressed air receiver may, without any extra dimensioning, be made so large, that the air pressure in the same may be kept practically constant, whereby the number of revolutions of the motor may be increased. The chief gain through this arrangement will bein spite of the somewhat increased work of pumping-a considerably increased effective average pressure, and thus a considerably increased eifect. In two-, threeor four-cylinder motors the weight of the motor for a certain eflect, and with it also the expense will thus be reduced.

The air pump may, of course, be constructed in any way desired, e. g. as a piston pump or as a fan, and it can be operated from the motor shaft, direct orby means of a suitable gear. Alternatively the pump may be worked by a separate motor.

In the accompanying drawing this invention is shown by way of example applied to two difierent motors, viz. in Fig. l to a four-cylinder motor and in Fig. 2 to a twocylinder motor.

In the motor shown in Fig. 1 compressed air enters the closed crank case 1 through a channel 2 from an air pump the piston 4 of which, movable in a cylinder 3, is operated from a crank 5 on the motor shaft 6.

In the motor shown in Fig. 2 the compressed air enters the closed crank case 1 through a channel 2 from a fan 7 the wheel 8 of which is operated from the motor shaft 6 by means of a toothed gear 10.

In both cases the compressed airas is usual-enters the working chambers in the motor cylinders 11 through channels in projections 12 existing on the cylinders.

Having now described my inventi0n,What I claim as new and desire to secure by Letters Patent is:

In a two-stroke internal combustion engine, the combination With a plurality of engine cylinders, of a crank case common to all the cylinders, means for supplying compressed air to said crank case, and means afl'ording communication between the c'ank case and the several engine cylinders and through which compressed air passes directly from the crank case to all of the cylinders.

In Witness whereof I have hereunto set my hand.

ANDERS HARALD RO SBORG. 

